1. Field of the Invention
The present invention relates generally to automatic steering apparatus for marine vessels, the control circuit, or a part thereof is doubled, that is, two control circuits which are the same in construction are provided. More particularly, this invention relates to automatic steering apparatus having dual steering control circuits in which various kinds of setting values, (i.e. data and the like) with respect to the automatic steering of a ship can be interchanged between both dual steering control circuits while the data can be preserved therein, during switch over in use between the two control circuits.
2. Description of the Prior Art
The known automatic steering apparatus of this kind is illustrated, for example, in FIG. 1 in which the main portion of a steering control circuit is doubled, that is, constructed of two identical steering control sections 10 and 20.
The steering control sections 10 and 20, are provided common bus lines BUS through each of which CPUs (central processing units) 11 and 21 are connected to ROMs (read-only memories) 12 and 22, RAMs (random access memories) 13 and 23, I/O (input/output) controllers 14 and 24 and D/A (digital-to-analog) converters 15 and 25, respectively, Rudder servo amplifiers 16 and 26 are connected respectively to the D/A converters 15 and 25.
Since the circuit elements, as mentioned above, duplicate the main hardware portions of the control circuit, even if trouble occurs in one control circuit, the other control circuit may be used to carry out the steering. Consequently, this steering apparatus is deemed high in reliability.
Further, an indicating/setting section 30 is mounted on the upper panel portion (not shown) of the automatic steering apparatus. This indicating/setting (I/S) section 30 is provided with a general-purpose display 31, a keyboard 32 and similarly known input/output devices. This indicating/setting section 30 is powered when one of the steering control sections 10 and 20 is operated as is arranged to function under the control of the steering control section 10 or 20 that is operated.
The indicating/setting section 30 is used to set various kinds of functions such as setting a course, limiting a steering angle, setting an off-course alarm, setting a ship's speed pulse rate and the like which are carried out by the automatic steering apparatus. Further, various kinds of control parameters in the automatic steering such as a counter rudder, a rudder angle ration, a weather helm adjustment and so on must be changed at any time in response to the shape of a ship's hull, the condition of cargo loaded in the ship, the weather and so on. These changes are made manually in the indicating/setting section 30, too. However, when the automatic steering apparatus is constructed such that the control parameters are assumed automatically from the ship's response, relative to the rudder angle, these changes in settings are not necessary and power-saving steering in which the hull, the condition of cargo and so on are automatically taken into consideration and their function may be carried out automatically.
Suitable switch means may be provided with automatic steering apparatus constructed as shown in FIG. 1 to first select which of the steering control sections 10 and 20 is to be used initially and which is to be used as a secondary stand-by. Assuming that the steering control section 10 is primary selection, automatic steering apparatus is actuated, then the CPU 11 reads initial values of various kinds of setting values from the ROM 12 and sets the readout initial values in the RAM 13 at the storage areas of the respective set values. Thereafter, the CPU 11 starts the calculation and the control for the steering of ship in accordance with the program stored in the ROM 12. In the automatic steering mode, the CPU 11 supplies a rudder angle command to the rudder servo amplifier 16 through the D/A converter 15.
When a new setting value is inputted automatically by the indicating/setting section 30, the CPU 11 reads such setting value through the I/O controller 14 and replaces the same with the previously set value that is stored in the RAM 13. Further, when the setting values of the control parameters such as the rudder angle ratio, the counter rudder and so on, in the automatic steering mode, are changed or when newly estimated values are obtained, the CPU 11 replaces the previously estimated values stored in the RAM 13 with the above newly estimated values.
In the foregoing situation, the secondary steering control section 20 that was not selected is not powered and is inoperative.
When the ship is steered by the primary steering control section 10, and then switched to the secondary steering control section 20 because of trouble occuring in the primary steering control section 10, or due to other reasons, the power of the primary steering control section 10 must be cut and the steering control section 20 powered. Thus, the CPU 21 in the steering control section 20 becomes actuated and responsive to the initial setting values, such as setting a course, limiting a rudder angle, etc., and the various kinds of control parameters such as the rudder angle ratio and, the counter rudder, as originally stored in the ROM 22. As a result, the setting values and control parameters for operating the secondary control section 20 are at values different from the values controlling the steering control section 10 prior to its being switched which values are all lost on cut off power to steering control section 10. Therefore, when the steering control sections are switched from one to the other, these values and parameters must be set again to remain on the correct course. Further, on cut off of power, all control parameters in the automatic steering operation are returned to the initial values, and remain at such values until they are reset or until the correct value is obtained. Consequently the course keeping and course changing properties of the known automatic steering apparatus are defective and also power saving steering can not be made. This defect is very serious.
Accordingly, although the steering control sections may be switched from one to the other, in order that the last setting values, the control parameters and the like can be used continuously as they have been determined, prior to the switch, the dual steering control sections must be both powered and the necessary data must be transmitted at all times from the primary steering control section to the standby steering control section, although it is normally inactive. FIG. 2 shows an example of the prior art automatic steering apparatus constructed as described just above.
Referring to FIG. 2, when the marine automatic steering apparatus is actuated, both steering control sections 10 and 20 are powered and a data exchange signal line SL is provided between the I/O controllers 14 and 24 in order that the necessary data can be transmitted and received between both steering control sections 10 and 20. Other portions are formed the same as those in FIG. 1. Hence, they are identified by the same reference numerals and need not be described in detail.
Though not shown, the power source provided for the automatic steering apparatus is backed up by a battery in order to prevent the last setting values and the last control parameters from being lost, even if power interruption occurs.
In the prior art automatic steering apparatus shown in FIG. 2, however, when the dual steering control sections are switched from one to the other, in order that the last setting values and control parameters and the like are transmitted and received between the two steering control sections, both steering control sections must be powered. Thus, in order to prevent the data from being lost even when the power interruption occurs, the power source of both steering control sections must be backed up by the battery. As a result, power consumption is increased because in the operation mode the standby steering control section is powered constantly. Since both the dual steering control sections are powered, both steering control sections deteriorate in quality simultaneously. Thus, as compared with the system in which only the steering control section being operated is powered, the prior art automatic steering control apparatus shown in FIG. 2 is lower in reliability. Further, when the power source of the entire apparatus is turned off, the last setting values and control parameters, etc., are lost.
Accordingly, it is an object of this invention to provide an improved marine automatic steering apparatus having dual steering control sections which overcome the shortcomings encountered with the prior art marine automatic steering apparatus.
It is another object of this invention to provide an improved marine automatic steering apparatus having dual steering control sections in which during operation, the last data and control parameters can always be used, notwithstanding switch-over from primary to secondary sections.
It is further object of this invention to provide a marine automatic steering apparatus having dual steering control sections in which various kinds of setting values, data and the like can be transmitted and received between both of the dual steering control sections.
It is still further object of this invention to provide a marine automatic steering apparatus having dual steering control sections in which the power consumption is prevented from being increased, the operational characteristics are prevented from being lowered and the steering efficiency after the steering control sections are switched from one to the other is prevented from being deteriorated even temporarily.